This invention relates to an improved mold for disc molding and more particularly to an apparatus for holding a stamper in which video or audio signals are memorized with or without grooves.
Japanese published patent application No. 58-58214 and Japanese laid open patent No. 59-230731 relate to injection mold apparatus. In these inventions, a stamper is clamped in a cavity so that an outer stamper holder holds an outer periphery of the stamper and an inner stamper holder holds an inner periphery of the stamper. When discs are formed by injection molding in a factory, several kind of discs are formed by injection molding in a day, and consequently stamper is changed several times a day. In some factories, the stamper is changed 5-6 times in a day.
In the prior art, when changing the stamper, the stamper is held by the hands of a worker. Namely, after opening mold halves and unfastening bolts which tightens the outer stamper holder to outer periphery of the stamper, the outer stamper holder is removed from the mold half. As the surface of the cavity of a disc mold is finished such as a mirror surface, scratch is easily formed. Therefore, when removing the outer stamper holder, careful working is required. As a result, it takes time to change the stamper. In case scratches are formed, it brings bad effect in transcribing the information on the video, audio memory disc. It is impossible to mold the disc with fine video or memory.
It is, therefore, an object of the present invention to provide an improved injection molding machine for molding discs, which permits to detach and install automatically the outer stamper holder.